Everyone seems to have a replacement for JavaScript - Google even has two. Now Microsoft has revealed that Anders Hejlsberg has been working on a replacement and it has released a preview of TypeScript.

TypeScript is open source - Apache 2.0 license -- and a superset of JavaScript. As you would expect from a Hejlsberg language it incorporates type checking, interfaces and lots of syntactic sugar.

The good news is that it is compatible with JavaScript - you can simply load JavaScript code and run it. JavaScript programs are TypeScript programs. The TypeScript complier outputs JavaScript so compiling a JavaScript program is just a pass though operation. To improve on JavaScript, TypeScript lets you include annotations that allow the compiler to understand what objects and functions support. The annotations are removed by the compiler, making it a zero overhead facility.

It also adds a full class construct to make it more like traditional object oriented languages. Not every JavaScript programmer will be pleased about the shift in emphasis, but the way it compiles to a JavaScript constructor is fairly transparent.

A class in TypeScript (above)- and what it compiles to (below)

You can see a video of Anders Hejlsberg explaining the pros of Typescript below:

Microsoft has a Visual Studio add-on to handle TypeScript projects complete with intellisense etc. In addition there are now syntax files for Sublime, Emacs and Vim.

This announcement explains quite a few things. It explains why Hejlsberg made so many cutting comments about JavaScript at June's Lang.NEXT. It also suggests that the father of C# has found other things to interest him. Since Windows 8 was announced it has been clear that a shift of power within Microsoft has made C#, and the whole .NET system, look less attractive - you could say that the re-imagining of Windows brought the limelight back on C++. This is probably a good time for Heljsberg to focus on improvements to the most used language on the planet and make it fit for large applications.

It might make sense for Heljsberg, but it might make less sense for the rest of us. There are already enough alternatives to JavaScript and only time will tell if the appropriate response is a big yawn or something more excited. The one big edge that TypeScript has is the promise of improved tools. Visual Studio is a good IDE and it might be enough to make TypeScript attractive.

At this early stage it is difficult to see the development as good. It isn't particularly good for JavaScript developers who already have alternatives, and it isn't good for C# developers who now have confirmation that Anders Hejlsberg is looking elsewhere.

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